Micro-Electro-Mechanical System Vapor Cells With Passivated Internal Cavities

TL;DR

This paper introduces a low-temperature bonding method for MEMs vapor cells with internal passivation using OTS coating, enabling improved quantum sensor performance by reducing electric fields and preventing Cs wall sticking.

Contribution

It presents a novel low-temperature bonding scheme compatible with internal OTS coating for MEMs vapor cells, addressing longstanding coating and bonding challenges.

Findings

Spectral linewidths of ~300 kHz achieved

Electric fields within vapor cells are kept below 10 mV/cm

Coating prevents Cs from sticking to the walls

Abstract

Micro-Electro-Mechanical, so called 'MEMs,' vapor cells are a key component in atom-based quantum sensors, such as clocks, gyroscopes, electric field sensors and magnetometers. MEMs vapor cell fabrication for Rydberg atom radio frequency sensors is particularly demanding. The Rydberg states used for the sensor can shift in a constant electric field which can be generated by the internal surfaces of the vapor cell cavity. The ratio of the detection wavelength to vapor cell size can span a large range, meaning that the radio frequency field-vapor cell interaction is a critical design consideration. In many radio frequency sensing cases, there is a desire to minimize the interaction between the vapor cell and the target radio frequency field, as well as assure that every vapor cell behaves uniformly. These criterion favor MEMs vapor cells with low background electric fields. Known inert, organic coatings cannot survive the bonding temperatures required for conventional anodic bonding of a MEMs vapor cell. Applying inert, organic coatings to the internal cavities of MEMs vapor cells is a longstanding challenge. In this paper, we present a low temperature bonding scheme that is compatible with coating the internal cavity of a MEMs vapor cell with Octadecyltrichlorosilane (CH$_3\,$(CH$_2$)$_{17}\,$SiCl$_3$, OTS). The coating prevents the Cs used in the vapor cell from sticking to the walls. Spectral linewidths of $\sim300\,$kHz are obtained using Rydberg spectroscopy, with energy shifts corresponding to electric fields $<$10$\,$mV$\,$cm$^{-1}$.